1. Field of the Invention
The present invention relates to a heat exchanger device in a gas-heated apparatuses used for the heat treatment of foodstuffs, the heat exchanger device having a fan wheel for the forced circulation of a treatment medium, a gas burner and at least one heat exchanger pipe surrounding the fan wheel.
2. Description of the Related Art
A heat exchanger apparatus of this type is disclosed in EP 0 526 768 B1. The burner therein is designed as a Bunsen burner and comprises a venturi pipe into which gas from a gas nozzle is blown. Air is entrained in the venturi pipe on account of the distance between the venturi pipe and the gas nozzle, so that a certain premixing of air and gas occurs. In this case, the burner is arranged upstream of the heat exchanger pipe, with the result that the relatively long flame which leaves the burner penetrates into the heat exchanger pipe and in the process also sucks up secondary air. A disadvantage of this design is the fact that a very long flame is produced which requires a first, rectilinear section of the heat exchanger pipe, if this flame is to be formed in an exact manner. In addition, a considerable noise is produced at the two suction points for air. When this apparatus is used for the heat treatment of foodstuffs, the noise causes a considerable annoyance in the rooms where appliances of this type are installed. Furthermore, this type of burner design requires continuous pressure monitoring of both the air pressure and the gas pressure and monitoring of the quantities fed in, which necessitates an extensive regulating device. Since this prior art device requires a rectilinear heat exchanger pipe section which is as long as possible for receiving the comparatively long flame and requires an air chamber having raised air pressure for supplying the primary and secondary combustion air, the burner is arranged at a relatively large distance from the fan wheel to accommodate these requirements. Accordingly, the hottest point of the heat exchanger apparatus in which the burner flame is situated does not lie directly next to the fan wheel and this part of the heat exchanger apparatus is not acted upon directly by the medium flow produced by the fan wheel.